Preserving the beauty of a cotton boll

Posted by | November 11, 2019 | cotton, ERS, Extension Activities, Research, Uncategorized | No Comments

Do you struggle with gift ideas? I do.

So there is a meeting coming up and we want to get the speakers something to remember it by. What do you get them? What says thank you and here is something to remember us by? Now I hate these sort of decisions, but in this case, given it was a meeting about cotton, I thought what about a locally grown cotton boll encased like a paperweight!

Taking something white and fluffy and making it last forever.

So armed with an idea and some locally grown cotton I just need to encase it in something.

Armidale grown cotton. What better to remember a local conference by?

Should be easy I thought.

I spoke to a colleague who is often making pens out of soil and who recently made me some soil clock faces. His resin of choice is Epoxy, but he warned me that I may have issues with it as I was not just impregnating the material with it, but wanted to encase it. The trouble here is that epoxy generates heat as it sets and the more you have the more heat it makes, sometimes causing the resin to boil. He also warned me that it tends to be a little yellow, but there was some available and we could try. So I ordered some square silicon cake moulds, big enough to hold a mature cotton boll and got ready.

OK, so nothing is perfect first time out.

When the moulds arrived they were square, but not cubic, which was a bit disappointing. Any way, we attempted the first boll casting and the fibres became see through, but the cotton was encased in a permanent and somewhat yellow resin. Encouraged, I ordered cubic moulds and brought a ‘clear casting epoxy’ for around $450 a kg of resin with the associated hardener.

The expensive epoxy arrived and so did my new cubic moulds. I got to work with some of my cotton bolls, but the results were disappointing.

The cotton was still becoming transparent, the resin had to be poured in a minimum of three layers to stop it boiling, which left lines on the finished cast and it was still yellow, not water clear at all. 

Disheartened, but not despondent.

So, up until now, I had been reading all about epoxy, but at this point I stumbled across a website that suggested for larger encasing projects polyester may be better suited. OK, so a bit more reading was needed, a new supplier was found and I tentatively ordered a kg of polyester and the not so nice MEKP catalyst. This set me back about $100 for the polyester, the catalyst and the shipping.

It arrived, I relocated my casting equipment to a fume hood and attempted my first cast. The boll floated, the fibres still became transparent, but the resultant cast was clear, sticky and only slightly lumpy on the surface. An improvement?

Overcoming the final hurdles.

So, the transparent nature of the fibres was annoying me. I’d read that permeable material mount better when coated with PVA or something similar. So a $5 bottle of PVA was obtained, poured into a cup, the cotton bolls dipped and then dried at 60oC in an oven using bulldog clips to stop them sticking to the oven shelves. Turns out this was quite effective, but a couple of dip and drying cycles or the use of the vacuum manifold were needed to get the cotton looking white post casting.

polyester and PVA – a recipe for success?

The polyester was also getting easier to work with in the fume hood. I’d pour a layer to lift the boll off the bottom of the mould, then another about an hour later into which the PVA coated boll was set and then a final pour an hour later again to fill the mould and cover the boll.

These were left for 12-16 hours to cure, then recovered from the mould, trying not to touch the sticky surface as it left finger prints and transferring the cast to the oven for a few hours to overcome this.

Another issue was a slight rippling on some surfaces despite using mould stripper. This was removed with wet/dry sand paper and an orbital sander. Working through grades from 280, 400, 600, 800 and 1000 grit the cubes were sanded down with a bowl of soapy water used to regularly wash the sides. It would take about 2 hours to work through 6 cubes in this way. Once sanded, the surfaces had lost their clarity so we did try some diamond polishing, which worked like a charm, but similar results were obtained in less time with both Turtle Wax scratch and swirl remover and Brasso. I simply mounted a microfiber cloth onto the orbital sander, applied one of these polishes and then, with the sander on, applied the sanded face of the cube against the cloth with a relatively firm pressure. After polishing each face for about 30 seconds followed by a light polish with a clean cloth a suitable finish was obtained.

Yellow epoxy, boiled epoxy and finally a fluffy white polyester boll!

So if you want to make a cotton paperweight or souvenir

Pick a good sized cotton boll with the lint still held by the bracts.

Dip the boll in PVA and then allow it to dry before applying a second PVA coat. You can dilute the PVA with water about 1 to 2 if needed.

Ensure you have either a silicon mould big enough to hold the boll or make a Perspex casting tray and apply a little mould stripper to the inside.

Mix your first batch of polyester resin, being mindful of the hazards associated with the products.

Pour a base layer to lift your boll off the bottom.

Just as this starts to go off (20-60 minutes) pour a second layer into which you set your PVA encased boll.

As this starts to set (another 20-60 minutes), prepare more polyester and top up the mould.

Allow it to cure, remove from the mould and harden in an oven.

Polish the surfaces, if needed, using wet/dry sand paper working toward a final grade of 1000 grit or higher. Consider reversing the paper for a very fine polish.

Finish the surface with a car polish or Brasso and enjoy your fixed boll.

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